Aerodynamic Performance Of Airfoil Research Articles

A Small Disturbance Model for Transonic Flow of Pure Steam With Condensation

A small-disturbance model to study transonic steady condensing flow of pure steam around a thin airfoil is developed. Water vapor thermodynamics is described by the perfect gas model and its dynamics by the compressible inviscid flow equations. Classical nucleation and droplet growth theory for homogeneous and nonequilibrium condensation is used to compute the condensate mass fraction. The model is derived from an asymptotic analysis of the flow and condensation equations in terms of the proximity of upstream flow Mach number to 1, the small thickness ratio of airfoil, the small quantity of condensate, and the small angle-of-attack. The flow field may be described by a nonhomogeneous and nonlinear partial differential equation along with a set of four ordinary differential equations for calculating condensate mass fraction. The analysis provides a list of similarity parameters that describe the flow physics. A numerical scheme, which is composed of Murman and Cole's algorithm for the computation of flow parameters and Simpson's integration method for calculation of condensate mass fraction, is applied. The model is used to analyze the effects of heat release due to condensation on the aerodynamic performance of airfoils operating in steam at high temperatures and pressures near the vapor–liquid saturation dome.

Passive flow control of a stalled airfoil using an oscillating micro-cylinder

The effect of passive flow control using an oscillating micro-cylinder near the leading edge of a stalled airfoil (S809) at a Reynolds number of 1 × 106 is numerically investigated. A physical analysis of the flow fields is performed to illustrate the mechanisms of flow control for the improvement of airfoil aerodynamic performance. When the optimal parameters are selected, the research about the ability of suppressing the separation of the static micro-cylinder is studied at different angles of attack. The simulation results show that the static micro-cylinder can effectively suppress the flow separation and improve the aerodynamic performance of airfoil at angles of attack range from 10° to 24°. Then we replaced the static micro-cylinder with the oscillating one. The simulation results proved that when a static micro-cylinder cannot control the flow separation well, a better flow control effect can be achieved by the oscillating cylinder. Furthermore, the diameter of the oscillating micro-cylinder is smaller than the static one's when a same lift-to-drag ratio is achieved. Compared with the original S809 airfoil, the lift-to-drag ratio of the airfoil with an oscillating micro-cylinder can be increased by 88.21% at optimal oscillate method.

Flow Physics behind the Effects of Leading-edge Protuberances on the Airfoil Aerodynamic Performance

This paper presents a numerical investigation of the flow physics behind the effects of leading-edge protuberances on the airfoil aerodynamic performance utilizing vortex dynamic method. An improved delayed detached eddy simulation (IDDES) method was adopted and validated through the comparisons with experimental results. Utilizing the IDDES scheme, together with vortex dynamic analysis, investigations were focused on the attached and post-stall regions, respectively. It was found that, within the attached region, the generation and development of the dominant diffused spanwise vortex rings over tubercled airfoil was responsible for the subsequent airfoil performance; within the post-stall region, the impaired flow detachment around both peak and trough sections of tubercles, due to the enhanced momentum injection by the strong streamwise vortices, resulted in better airfoil aerodynamic performance.

Effect of Gap between Airfoil and Embedded Rotating Cylinder on the Airfoil Aerodynamic Performance

Effect of Gap between Airfoil and Embedded Rotating Cylinder on the Airfoil Aerodynamic Performance

The flow separation development analysis in subsonic and transonic flow regime of the laminar airfoil

Abstract Wind tunnel tests of a laminar airfoil have been performed at the Institute of Aviation in Warsaw. The main goal of the investigation was to study the separation process development in subsonic and early transonic flow regime. The airfoil chord was 0.2m. During wind tunnel test the natural laminar-turbulent transition was applied. The Mach numbers were 0.3 and 0.7. Reynolds number were approximately equal to 1.22.106 and 2.85.106 respectively. The angle of incidence was increased up until the flow was fully separated. During the experimental research, chosen test methods such as pressure measurements and schlieren visualization were applied. Wind tunnel results were analyzed in terms of aerodynamic coefficients and flow separation type identification. The wind tunnel investigation revealed that separation phenomena at subsonic and transonic flow regime affected in a different manner on the airfoil aerodynamic performance. This was mainly because of the change of the flow pattern influencing on the separation process.

Passive flow control of a stalled airfoil using a microcylinder

The effect of passive flow control using a microcylinder near the leading edge of a stalled airfoil (NACA 0012) at a Reynolds number of 6 × 106 is investigated through a computational study. Detailed parametric analyses for the microcylinder are carried out based on Reynolds averaged Navier-Stokes (RANS) calculations in order to determine the optimal control parameters. Computations using delayed detached eddy simulation (DDES) for the controlled and uncontrolled cases are supplemented to capture the transient vortical structures in the massive separation region and further verify the numerical results from RANS. It is found that the total aerodynamic forces of the entire system are highly sensitive to the spacing between the surfaces of the airfoil and the microcylinder. When a superior set of control parameters is adopted, significant enhancement of lift coefficient and lift-to-drag ratio can be achieved after stall, accompanying a pronounced decrease of drag coefficient. Both RANS and DDES results indicate that the heavy stall can be effectively delayed and the extent of large separation region on the airfoil suction surface can also be diminished by such a little control device. A physical analysis of the flow fields is performed to illustrate the mechanisms of flow control for the improvement of airfoil aerodynamic performance.

Aerodynamic Analysis of an Airfoil With Leading Edge Pitting Erosion

Leading edge erosion is a considerable threat to wind turbine performance and blade maintenance, and it is very imperative to accurately predict the influence of various degrees of erosion on wind turbine performance. In the present study, an attempt to investigate the effects of leading edge erosion on the aerodynamics of wind turbine airfoil is undertaken by using computational fluid dynamics (CFD) method. A new pitting erosion model is proposed and semicircle cavities were used to represent the erosion pits in the simulation. Two-dimensional incompressible Reynolds-averaged Navier–Stokes equation and shear stress transport (SST) k–ω turbulence model are adopted to compute the aerodynamics of a S809 airfoil with leading edge pitting erosions, where the influences of pits depth, densities, distribution area, and locations are considered. The results indicate that pitting erosion has remarkably undesirable influences on the aerodynamic performance of the airfoil, and the critical pits depth, density, and distribution area degrade the airfoil aerodynamic performance mostly were obtained. In addition, the dominant parameters are determined by the correlation coefficient path analysis method, results showed that all parameters have non-negligible effects on the aerodynamics of S809 airfoil, and the Reynolds number is of the most important, followed by pits density, pits depth, and pits distribution area. Meanwhile, the direct and indirect effects of these factors are analyzed, and it is found that the indirect effects are very small and the parameters can be considered to be independent with each other.

Microtab Design and Implementation on a 5 MW Wind Turbine

Microtabs (MT) consist of a small tab placed on the airfoil surface close to the trailing edge and perpendicular to the surface. A study to find the optimal position to improve airfoil aerodynamic performance is presented. Therefore, a parametric study of a MT mounted on the pressure surface of an airfoil has been carried out. The aim of the current study is to find the optimal MT size and location to increase airfoil aerodynamic performance and to investigate its influence on the power output of a 5 MW wind turbine. Firstly, a computational study of a MT mounted on the pressure surface of the airfoil DU91W(2)250 has been carried out and the best case has been found according to the largest lift-to-drag ratio. This airfoil has been selected because it is typically used on wind turbine, such as the 5 MW reference wind turbine of the National Renewable Energy Laboratory (NREL). Second, Blade Element Momentum (BEM) based computations have been performed to investigate the effect of the MT on the wind turbine power output with different wind speed realizations. The results show that, due to the implementation of MTs, a considerable increase in the turbine average power is achieved.

Numerical study of the aerodynamic performance of blunt trailing-edge airfoil considering the sensitive roughness height

For rough wind turbine airfoil and its blunt trailing-edge modification, the aerodynamic performance has been numerically investigated to facilitate a greater understanding of the effects of the blunt trailing-edge modification on the aerodynamic performance enhancement of airfoil with sensitive roughness height. The S834 airfoil from National Renewable Energy Laboratory is used for the simulation. The lift and drag coefficients of S834 airfoil with smooth or rough surface are calculated by the k-ω SST turbulence model, and are compared with wind tunnel test results. The aerodynamic performance of airfoils with different roughness heights is studied to obtain the sensitive roughness heights of suction and pressure surfaces. The mathematical expression of the blunt trailing-edge airfoil profile is established using the coordinate's rotation combined with the zoom coefficient of coordinate. Then, the S834 airfoil with sensitive roughness height is modified to be symmetrical blunt trailing-edge modification, and the lift and drag coefficients and the lift-drag ratio are also calculated and analyzed. Results indicate that the sensitive roughness height of suction surface is 0.5 mm, and the pressure surface is insensitive to the roughness height. Through the blunt trailing-edge modification, the lift coefficient and the maximum lift-drag ratio obviously increase for rough airfoil, and the sensitivity of airfoil to roughness height is reduced. The research provides significant guidance for designing the wind turbine airfoil under conditions of rough blade.

High Humidity Aerodynamic Effects Study on Offshore Wind Turbine Airfoil/Blade Performance through CFD Analysis

Damp air with high humidity combined with foggy, rainy weather, and icing in winter weather often is found to cause turbine performance degradation, and it is more concerned with offshore wind farm development. To address and understand the high humidity effects on wind turbine performance, our study has been conducted with spread sheet analysis on damp air properties investigation for air density and viscosity; then CFD modeling study using Fluent was carried out on airfoil and blade aerodynamic performance effects due to water vapor partial pressure of mixing flow and water condensation around leading edge and trailing edge of airfoil. It is found that the high humidity effects with water vapor mixing flow and water condensation thin film around airfoil may have insignificant effect directly on airfoil/blade performance; however, the indirect effects such as blade contamination and icing due to the water condensation may have significant effects on turbine performance degradation. Also it is that found the foggy weather with microwater droplet (including rainy weather) may cause higher drag that lead to turbine performance degradation. It is found that, at high temperature, the high humidity effect on air density cannot be ignored for annual energy production calculation. The blade contamination and icing phenomenon need to be further investigated in the next study.

The effect of variations in first- and second-order derivatives on airfoil aerodynamic performance

ABSTRACTThe geometric factors which influence airfoil aerodynamic performance are attributed to variations in local first- and second-order curvature derivatives. Based on a self-developed computational fluid dynamics (CFD) program called UCFD, the influence of local profile variations on airfoil aerodynamic performance in different pressure areas is investigated. The results show that variations in first- and second-order derivatives of the airfoil profiles can cause fluctuations in airfoil aerodynamic performance. The greater the variation in local first- and second-order derivatives, the greater the fluctuation amplitude of the airfoil aerodynamic coefficients. Moreover, at the area near the leading edge and the shock-wave position, the surface pressure is more sensitive to changes in first- and second-order derivatives. These results provide a reference for airfoil aerodynamic shape design.

Analyzing the effect of wind tunnel wall on the aerodynamic performance of airfoils

This paper analyzes the effect of wind tunnel wall interference on the airfoil aerodynamic performance, based on the results of experiment and CFD numerical simulation. The experimental measurement was made in IET using the low-speed and closed wind tunnel. The airfoil was DU91-W2-250. The numerical simulation with tunnel wall (wall), without tunnel wall (no wall) and without side tunnel wall (no side wall) were performed. Through the comparison the results between Exp and CFD, it is feasible to use CFD numerical simulation in this paper. And we get the following conclusions: the upper and lower tunnel walls make the flowing area decrease and the velocity increase due to the thickness of boundary layer on the walls, and they also casuse that C l and C d increase. The side tunnel walls cause span-wise flowing and delay the flow separation on the surface of airfoil, meanwhile, they cause that the velocity decreases, C l decreases and C d increases. At small angles of attack, the effect of side tunnel walls on the flowing of airfoil surface can be neglected. However, this effect is very significant at large angles of attack. The classical method can not work well at large angle of attacks for the correction of wall interference in wind tunnel because it doesn’t consider the effect of tunnel wall boundary layer. The C l should be increased through the correction, meanwhile, it is found that the flowing is not two-dimensional flow at large angles of attack in the free-air condition, so we suggest that the pressure measurement with more cross sections or using balance method should be used to obtain the aerodynamic performance of airfoil.

Numerical simulation of airfoil aerodynamic performance under the coupling effects of heavy rain and ice accretion

It has been widely investigated before that both heavy rain and icing conditions can cause severe aerodynamic performance penalties to aircraft in flight; however, aircraft aerodynamics in the presence of both heavy rain and ice accretion has been little explored so far. In this article, a numerical simulation is performed to study the aerodynamic performance of an iced NACA 0012 airfoil in simulated heavy rain condition. A two-way momentum-coupled Eulerian–Lagrangian two-phase flow approach is developed to simulate raindrop trajectories in the airflow field. The analysis indicates that both rain and ice can separately cause severe aerodynamic performance degradation to the airfoil at most angles of attack of interest. In the presence of both ice and rain, a further severe aerodynamic penalty can be produced by rain based on the ice-induced aerodynamic performance degradation. Premature boundary-layer separation and boundary-layer momentum losses by splashed-back raindrops are also observed.

Computational methods for investigation of surface curvature effects on airfoil boundary layer behavior

This article presents computational algorithms for the design, analysis, and optimization of airfoil aerodynamic performance. The prescribed surface curvature distribution blade design (CIRCLE) method is applied to a symmetrical airfoil NACA0012 and a non-symmetrical airfoil E387 to remove their surface curvature and slope-of-curvature discontinuities. Computational fluid dynamics analysis is used to investigate the effects of curvature distribution on aerodynamic performance of the original and modified airfoils. An inviscid–viscid interaction scheme is introduced to predict the positions of laminar separation bubbles. The results are compared with experimental data obtained from tests on the original airfoil geometry. The computed aerodynamic advantages of the modified airfoils are analyzed in different operating conditions. The leading edge singularity of NACA0012 is removed and it is shown that the surface curvature discontinuity affects aerodynamic performance near the stalling angle of attack. The discontinuous slope-of-curvature distribution of E387 results in a larger laminar separation bubble at lower angles of attack and lower Reynolds numbers. It also affects the inherent performance of the airfoil at higher Reynolds numbers. It is shown that at relatively high angles of attack, a continuous slope-of-curvature distribution reduces the skin friction by suppressing both laminar and turbulent separation, and by delaying laminar-turbulent transition. It is concluded that the surface curvature distribution has significant effects on the boundary layer behavior and consequently an improved curvature distribution will lead to higher aerodynamic efficiency.

Effects of cowling design on aerodynamic performance of airfoil with BLI

Effects of cowling design on aerodynamic performance of airfoil with BLI

Artificial intelligence metamodel comparison and application to wind turbine airfoil uncertainty analysis

The Monte Carlo simulation method for turbomachinery uncertainty analysis often requires performing a huge number of simulations, the computational cost of which can be greatly alleviated with the help of metamodeling techniques. An intensive comparative study was performed on the approximation performance of three prospective artificial intelligence metamodels, that is, artificial neural network, radial basis function, and support vector regression. The genetic algorithm was used to optimize the predetermined parameters of each metamodel for the sake of a fair comparison. Through testing on 10 nonlinear functions with different problem scales and sample sizes, the genetic algorithm–support vector regression metamodel was found more accurate and robust than the other two counterparts. Accordingly, the genetic algorithm–support vector regression metamodel was selected and combined with the Monte Carlo simulation method for the uncertainty analysis of a wind turbine airfoil under two types of surface roughness uncertainties. The results show that the genetic algorithm–support vector regression metamodel can capture well the uncertainty propagation from the surface roughness to the airfoil aerodynamic performance. This work is useful to the application of metamodeling techniques in the robust design optimization of turbomachinery.

Experimental investigation of separation bubble control on an iced airfoil using plasma actuator

In this paper, the flow control on an iced airfoil has been experimentally studied by installation of DBD plasma actuator. Flow pattern and aerodynamic parameters of runback iced NACA 23012 airfoil have been studied at angles of attack close to stall and post-stall under plasma-on and plasma-off states at Re=0.6×106, and the results were compared with those of clean airfoil. It was found that by activating the plasma actuator upstream of the ice accumulation, the stall angle delays 2 degrees and the iced airfoil maximum lift coefficient increases about 6%. In addition, at 16° angle of attack, the airfoil lift to drag aerodynamic ratio (L/D) increases about 100%. Indeed, it is concluded that by controlling the separation bubble, the plasma actuator is almost able to eliminate the adverse effects of icing on the airfoil aerodynamic performance.

XFOIL vs CFD performance predictions for high lift low Reynolds number airfoils

Blade Element Momentum (BEM) theory is an extensively used technique for calculation of propeller aerodynamic performance. With this method, the airfoil data needs to be as accurate as possible. At the same time, Computational Fluid Dynamics (CFD) is becoming increasingly popular in the design and optimization of devices that depend on aerodynamics. For fixed and rotary wing applications, the airfoil lift over drag coefficient is the dominant airfoil performance parameter. Selecting a suitable computational tool is crucial for the successful design and optimization of this ratio. The XFOIL code, the Shear Stress Transport k−ω turbulence model and a refurbished version of k−kl−ω transition model were used to predict the airfoil aerodynamic performance at low Reynolds numbers (around 2.0×105). It has been shown that the XFOIL code gives the overall best prediction results. Also, it is not clear that CFD turbulence models, even with boundary layer transition detection capability, can compute better airfoil performance predictions data.

Roughness effect on airfoil aerodynamic performance for land-yacht robot

The land-yacht robot presented in this paper aims at an Antarctic expedition which is driven by wing-sail. The wing-sail is composed by airfoil and surface roughness, which is one of the main factors affecting the aerodynamic performance of the airfoil. In order to improve the efficiency of the airfoil, stress analysis of the wing-sail and airfoil mechanism is researched and the type of airfoil is determined. For roughness size, equivalent particle roughness is introduced and a boundary layer flow separation model is a simulated roughness model. Then N-S equations and the S-A turbulence model are predicted airfoil aerodynamics in CFD (Computational Fluid Dynamics). When different sizes of a roughness strip are deposed on an airfoil surface, we obtain lift and drag coefficient, sensitive angle of attack of 6°, and 0.5 mm of sensitive roughness size. When roughness is arranged at different positions, we discover two sensitive positions, 10% chord length in suction surface and near trailing edge in pressure surface. Further analysis of the two sensitive positions in 10% chord length and aerodynamic is worse with the increasing roughness size. Near the trailing edge, there is a threshold of 0.7 mm. Lower than 0.7 mm, aerodynamics is improving; in contrast, it is worse. Finally, simulation results are verified by experiments. It shows that the predicted value conforms to the experiments and this research can provide a valuable reference for the mechanism of the land-yacht robot.

Numerical Study of the Effect of Geometrical Changes on the Airfoil Aerodynamic Performance

Numerical Study of the Effect of Geometrical Changes on the Airfoil Aerodynamic Performance